Method and apparatus for molding thermoplastic materials



Patented May l, 1951 UNIED STATES TENT FFICE METHOD AND APPARATUS FORMOLDING THERMOPLASTIC P/KATERIALS 19 Claims.

This invention relates generally to a method and apparatus for moldingthermoplastic materials and has particular relation to a method andapparatus for molding thermoplastic materials oi he type having aplasticizing temperature which is only relatively slightly higher thanthe setting temperature of the material.

In the continuous injection molding of thermo'- plasticl materials ofthe type having a plasticizing temperature which is only relativelyslightly higher than the setting temperature of the material, one of theforemost diiculties encountered is the running, dripping and oozing ofthe iiuid thermoplastic material from the ejection end of the nozzleduring the successive molding operations when the nozzle is out ofcontact withl the mold. Various methods and means have been proposedheretofore for eliminating the dripping of the iiuid thermoplasticmaterial from the ejection end or" the nozzle, but to date none of thesemethods or meansl have enjoyed any extensive commercial use. Thus,various types of nozzle structures have been proposed which include theuse of various manually and automatically operated nozzle stops, orvalves or other orifice restrictions, which are intended to mechanicallystop the ow of the fluid thermoplastic material when the ejection end ofthe nozzle is out of Contact With the mold.

In the case of certain thermoplastic materials, particularly linearpolyamide condensation products such as those of the type knowncommercially as nylon, the relative temperature range between theplasticizing temperature and the setting temperature is only about 20 F.to 40 F., which amounts to about or less of the plasticizingtemperature.

Certain other thermoplastic materials have a relative temperature rangebetween the plasticizing temperature and the setting temperature whichamounts up to about 25% of the plasticizing temperature. One suchmaterial is polystyrene which has a setting temperature around 210 F. to220 E. and a plasticizing temperature around 280 F.

Thus, it has been a problem in the art to continuously injectthermoplastic materials of this type in that the material hardens andwedges in the nozzle passage if it has not been heated to theplasticizing temperature, and on the other hand, the material is in ailuid condition at the plasticizing temperature which results inrunning, dripping and oozing from the ejection 2 ber 23, 1944, nowPatent Number 21,460,831v that the ejection nozzle continuouslyaccumulatesA heat caused by leakage, densication and friction. It is thegeneral practice to heat the material receiving mold up to the uppersetting temperature range so that the thermoplastic material will notprematurely set in the sprues or runners of the mold before the moldcavity has been completely filled. In some cases, the ternperature ofthe mold is held relatively close `to' the temperature of the chamber,thus Causing the mold to contribute accumulating heat to the ejectionorice or" the nozzle, particularlywhen the nozzle and mold are incontact. Likewisait has been the practice in the art to maintain thechamber at a fairly high plasticizing tempera ture in order to preventthe material from setting and hardening in the chamber, wedging in thenozzle passageway, or both.

Accordingly, it is an object of the present invention to provide amethod and apparatus which will eliminate the many prior artv dicultiesand, in particular, will prevent the running and oozing of thermoplasticmaterials from the nozzle in continuous injection molding processes.

Another object of the invention is to provide a method and apparatuswhich will prevent the suction of fluid thermoplastic materials backintothe cylinder when the piston is withdrawn back into the cylinder.

Still another object is to provide a method and apparatus for theinjection molding of thermoplastic material wherein the material in theejection orifice is constantly maintained at its In my said Patent2,460,831, i have disclosed" and claimedV a method and apparatus for theinjection molding of thermosetting materials which involves thepressure-feeding of the' thermcse'tting material through4 a restricted1ejecting nozzle and removing accumulatingv heat'from* the nozzleWhenever the temperature of the nozzle rises above the plasticizingtemperature of the material to prevent the polymerization and setting ofthe material in the nozzle passage.

The present invention generally comprises the method of continuouslyinjecting a thermoplastic material having a plasticizing temperatureonly relatively slightly higher than its setting temperature into amaterial-receiving mold which comprises pressure feeding said materialinto a chamber, heating said material in said chamber to a plasticizingtemperature, pressure feeding said material from said chamber into andthrough an ejecting nozzle in the form of a substantially restrictedpassage, removing heat caused by leakage, densication and friction fromsaid nozzle whenever the temperature of the nozzle rises above thelowest plasticizing temperature of said material in order to maintainsaid material in a semi-fluid, plastic condition, and injecting saidmaterial at said temperature from said nozzle into saidmaterial-receiving mold. Additionally, the present invention generallyincludes a method and apparatus for the continuous molding ofthermoplastic material, involving an ejecting nozzle structure havingonly a slightly restricted and elongated passage associated with thechamber and terminating at its ejection end in a shoulder or transverseabutment wall provided with a relatively small ejection orifice, theabutment wall causing the accumulation of an insulating layer ofthermoplastic material in the annular corner dened by the passage walland the abutment wall. This layer serves to prevent the transmission ofheat from the nozzle passage to the ejection orice. Additionally, thepreferred ejecting nozzle structure preferably includes a coolingpassage disposed adjacent the ejection orifice or abutment wall, orboth, and adapted to provide for the iiow of a coolant iiuidtherethrough, and regulating means responsive to the temperature of thenozzle adjacent the orifice or abutment wall, or both, for controllingthe flow of the coolant whenever the temperature of the nozzle at thesepoints rises above the lowest plasticizing temperature of thethermoplastic maf terial.

Referring now to the drawings, there is shown in Fig. 1 an injectionmolding apparatus together with a mold cavity for molding thermoplasticmaterial. In general, this apparatus comprises a heating andplasticizing chamber wherein the thermoplastic material is preheated toa temperature which renders it plastic and fluid. This plasticizingchamber is maintained below the burning temperature of the thermoplasticmaterial and generally considerably above its lowest plasticizingtemperature. Thus, in the case of linear poiyamides of the nylon typegenerally, the chamber is maintained between 550 F. and 700 F.,depending upon the flow characteristics of the material which generallyvary with the specific gravity thereof. Thus, in the case of arelatively stiff flowing material the plasticizing temperature in thechamber must be higher than is the case with a soft flowing materialwhich can be maintained in a plastic and fluid state at a somewhat lowertemperature.

A nozzle structure including an ejection orice is associated with theplasticizing cylinder and interconnects the chamber with the sprue ofthe mold by contact with the sprue bushing. This nozzle structure isdistinguished from conventional injection molding nozzles in that it isprovided with a cooling means and preferably with a thermocouple leadingto a thermostatic valve control device for maintaining the temperatureof the nozzle at the lowest plasticizing temperature of the material bymeans of regulating the flow of coolant into the cooling passage. Thus,the present method involves the dissipation of heat conducted to thenozzle from the plasticizing chamber and also dissipates accumulatingheat generated by the internal friction with the thermoplastic materialboth in the chamber and in the nozzle and also dissipates accumulatingfrictional heat caused by sliding contact of the material with the wallsof the chamber and nozzle. In addition, the present method provides forthe dissipation of accumulating heat in the nozzle caused by compressionand densication of the material in the chamber and in its passagethrough the nozzle.

In the drawing,

Fig. 1 is a longitudinal sectional view of an injection moldingapparatus adapted for use with my invention;

Fig. 2 is a view in section taken on line 2-2 of Fig. 1;

Fig. 3 is a longitudinal sectional view of an injection nozzle structureembodying my invention;

Fig. 4 is a view in section taken on line 4-4 of Fig. 3, and

Fig. 5 is a view in section taken on line 5-5 of Fig. 3.

Referring more particularly to the apparatus I0, the plasticizingchamber includes a cylindrical body II in which a piston I2 is adaptedto be reciprocated by any suitable mechanism, not shown, which mechanismmay be a hydraulic motor, for example. The piston is fluted intermediateits ends for permitting escape of fine particles of material frombetween the piston and cylinder walls. Thermoplastic material M is fedto the interior of the cylinder body I I through an opening I6 from ahopper I1, which is mounted over the opening I6. When the piston I2 isreciprocated in the cylinder it moves to the left of the opening I6 andmaterial drops into the cylinder and is moved toward the right by thepiston into the bore of a cylindrical body 20, which is securedintegrally with the member II. The body 20 is preferably provided with acooling system consisting of an internal passage 2I, through which acoolant, such as water, may be circulated. The passage 2I is in the formof a spiral and may be formed by cutting a spiral channel about the body20 and a complementary channel on the interior of the sleeve 24, whichis secured over the body 2| by threads and preferably locked in positionby a threaded collar 24a, as shown. The water enters the connection 22,which is connected with one end of the passage 2I, and circulatesthrough the passage 2I, then passing from the body 20 through aconnection 23. Also, the body 20 is adapted to be heated by heatingunits indicated at 25, which heating units may be of any suitableelectrical resistance material, or it may be heated by any suitablemeans. In the present embodiment, however, there are shown resistanceelements 26a embedded in ceramic material in the form of bandsencircling` the sleeve 24 and secured by bolts 26. The temperature ofthe member 20 is maintained approximately at a predeterminedtemperature, the particular temperature depending upon the type ofthermoplastic material used, and I have shown a thermocouple element 21,located in the body 20 so that it is responsive to the temperature ofthe body. The thermocouple',1n the present instance,

is part of a system for controlling energzation of the heater elements26. The control system, however, is not shown, as such systems are knownto those skilled in the art. Preferably, Vwater is circulated throughthe body 2U when the body temperature approaches the maximum (burning)temperature. This may be controlled thermostatically by suitable means,not shown. In 'one embodiment of the present method involving a nylontype thermoplastic material, the temperature of the body 20 wasmaintained at about 600 F. to 650 F., which is the optimum plasticizingtemperature range for maintaining the material M in a plastic, fluidcondition, substantially above its setting temperature vand below 'itsburning temperature.

A nozzle 30 is connected, as by screw threading, with the body 20 fordischarging the plastic material into the sprue of a mold 4B. The nozzle30 includes a neck portion 3l, a tapered, restricting entry passage 32and an ejection orifice 33 which is preferably of 'even diameter, asshown, but which may taper outwardly or flare in slight degree as shownin Fig. 3. Preferably, however, in one embodiment of the invention, thewalls leading from the plasticizing chamber to the entrance 0f the oriceare constructed as shown in Fig. 3.

An inlet connection 34 is connected to a coolant passage or opening 35formed in the neck portion 3| so that a cooling fluid, in the presentinstance water, may be led to the passage 35 and the water is dischargedtherefrom through an outlet connection 36. As shown, a thermostaticcontrol valve, indicated diagrammatically at 31, is placed in the inlet34 and is responsive to the temperature of the neck portion 3| of thenozzle forcausing the passage of water to the coolant passage 35 as thetemperature rises above the minimum temperature at which the `materialis plastic and semi-fluid, and cutting off the flow of coolant wheneverthe temperature lowers to the `setting temperature of the material. Itis essential to the successful practice of my invention that the coolingmeans, in the present embodiment the passage 35 and water circulationconnections and control means, be so designed vthat it can dissipateheat from the nozzle structure rapidly enough to change the physicalstate of the material from a plastic and fluid condition to asemi-fluid, plastic condition such that the material will not befree-running and yet will not be in a set, solid form.

A pair of thermocouple wells are provided, one on each side of thecoolant passage 35 for determining the temperature in the neck portion3l by means of thermocouples 38, one of which is connected to thecontrol valve 31. The selection as to which thermocouple to use dependsupon the nature of the material being molded. With Va free-runningmaterial of low specific gravity, it is advantageous to maintain thetemperature at the juncture of the tapered inlet 32 and the ejectionorifice 33 sumciently cool to cause the material to lose its extremefluidity at' that point and it is therefore necessary toaccuratelydetermine the temperature at that point. On the other hand, with certainthermoplastic materials such as styrene, it has been found sunicient tocontrol the now of coolant by virtue of the temperature directly alongthe ejection orifice 33.

In the preferred embodiment shown in Fig. 3, the nozzle structure isprovided with an inlet portion 32a which is only slightly tapered Yandwhich terminates in a shoulder or abutment Wall l39, the ejectionorifice 33 being similar to.

that shown in Fig. 1. Additionally, the inlet por-d tion adjacent theabutment wall 39 is preferably in cylindrical form as shown at 32h toassist in maintaining'an insulating barrier or layer M1. By means ofthis construction, the lines of force at the area defined by 32h and 39are all `perpendicular ror horizontal to the central longitudinal axisof the nozzle, which tends to make the barrier M1 substantiallypermanent once it has been built up. The function of this abutment wall39 is to retard and store material M1 during the molding operation so asto provide an insulating layer M1 which, according 'to my observations,serves to retard the passage of heat from the chamber l2, from the inlet`portion 32a and from the plastic, uid material M in the inlet portion32a. Thermoplastic materials appear to be poor conductors of heat andtherefore I have provided an excellent insulating barrier M1 which,although it is continuously being substituted by new material M at avery slow rate of substitution, is nevertheless ever present during themolding operation. Moreover, according to my observations, the taperedjuncture surface area S which is formed between the fast moving plastic,fluid material M and the slow moving insulating barrier M1, provides thesubstantially exact and perfect tapered configuration for the particularmaterial being molded. This discovery is set forth and claimed in mycopending application S. N. 75,057, filed February 7, 1949.

As shown in Fig. 3, I have provided alternate coolant passages 35a and35h and alternate thermocouplewells. By this means it is possible tocool the insulating barrier M1 to either a semifluid, plastic stage, orto a solid, plastic stage, or permit it to remain fluid and plastic, orcause it to become uicl and plastic.

The mold structure 40 which is formed of two parts 4| and 42 has a spruebushing 42a in the part 4l for directing the thermoplastic material tothe runners 43, formed in the chamber 42. The mold 4U is provided withmold cavities 44, the cavities in this instance being illustrated ascubes, although they may be of any desired form, depending upon'theshape of the article desired.

A sprue puller and 'knock-out'rod 45 is provided, which is operated bysuitable mechanism, after the mold part 42 has been separated from part4i following a molding operation, for pulling the sprue from the spruebushing 42a and then for knocking the sprue and its integral runnersfrom the part 42. Also, knock-out rods may be provided for removing themolded pieces from the cavities 44, but since such knock-out rods areWell known they have not been shown. It is to be understood that for thesake of clearness, the various'elements for supporting the mold and itsparts and the mechanism for operating the sprue puller 45 are not shown,as they may be of conventional design.

The mold 40 is maintained at a temperature approaching but below thesetting temperature of the thermoplastic material so that the materialwill not set and harden in the sprue, runners and mold before all thecavities in the mold have been completely filled. Thus, in instanceswhere the sprue or runners or mold cavities include relatively thinsections, it is necessary to maintain a somewhat higher mold temperature'than is the case with relatively large sections.

In the case of synthetic linear polyamides 'of the nylon type, with vasetting temperature 'of about 480 F., the mold is maintained at atemperature varying from325 F. to 475 F., depending upon the type ofnylon and the size of the mold sections.

The parts 4l and 42 have electrical resistance elements 46 embeddedtherein for heating the mold, although any other suitable heating meansmay be used, and the temperature of the mold is controlled by a suitablecontrol mechanism for the heating elements, which system includes athermocouple 4'! embedded in the part ft2 of the mold. The thermocoupleaffects the control system in a manner Well known in the art andtherefore this control system is not shown.

In the operation of the apparatus i9, the thermoplastic material M isplaced in the hopper I1, usually in a powdered or granulated condition,and the piston l2 is operated to move the material into the bore of thebody 20. rEhe material is heated in the body 28 to a plasticizingtemperature at which it becomes fluid and plastic. The sprue bushing 2aof the mold fl is maintained in contact with the nozzle and in alignmentwith the nozzle orifice. The part 42 of the mold is closed on part Lll,as shown in the drawing, and the piston l2 is then actuated to force theplasticized material M from the cylindrical body 2 into the entrypassage 32 of the nozzle where the material M is thence forced into andthrough the ejection orifice 33. Considerable heat is accumulated by thenozzle and the material in the nozzle due to the densication of thematerial in its passage through the nozzle. Also, considerable heat isaccumulated due to internal friction of the material and friction of thematerial being forced along and against the walls of the nozzle passage.This accumulating heat plus the heat leakage from the cylindrical body2G causes an increase in temperature in the nozzle and the material inthe nozzle. Thus, the material M in the ejection orifice 33 willnormally be fluid and will run, ooze and drip from the ejection orificewhen it is out of contact with the mold. However, the control valve 37is responsive to the temperature of the nozzle through an electricalcontrol circuit (not shown) connected to the thermocouple 38. Thecontrol circuit and valve are so regulated that whenever the temperatureof the nozzle rises above the lowest plasticizing temperature of thematerial at which it can be maintained in a semi-fluid, plasticcondition, the valve I will admit coolant into the coolant passage toremove the necessary amount of heat required to maintain the material ina semi-fluid, plastic state. In actual practice, I have found that byproper regulation, it is only necessary to cause the coolant to fiowintermittently in droplet forni into the passage 35 and this is the casewith an actual nozzle of the type shown in Figs. 3, 4 and 5 which isshown in exact working dimensions.

When material is forced against the abutment wall 39, it builds up andforms an insulating barrier M1 which prevents the transmission ofaccumulating heat to the ejection orifice 33. If the nozzle passage 32ais tapered up to the abutment wall 39, the material M1 is slowly butcontinually being forced out of the ejection orifice 33 and beingreplaced by fresh plasticized material M forced into the nozzle passage.If the nozzle passage area adjacent the abutment wall 39 is ofcylindrical form, as shown at 32h, I have found that the insulatingbarrier M1 formed during the molding operations is substantiallypermanent in character. In either event, a perfect taper configuration Sis formed by the barrier M1 and this barrier M1 serves as a part of thenozzle passage and thereby reduces the friction and resultingaccumulating heat.

The plasticized material M is forced out of the ejection orifice 33 andinto the mold through the sprue 62a, runners 43 and into the moldcavities 4d. The interior of the sprue and runners remains somewhatplastic for an interval and provides for the transmission of materialand pressure to the cavities until the material in the cavities has setand hardened. The piston acts upon the material during the setting ofthe material in the mold for maintaining the required pressure in themold cavities and to ll in any shrinkages. After setting has taken placein the mold, the force of piston l2 acting on the material is relievedand the mold part ll2 is removed from the part 4l. It has been foundthat, due to maintaining the temperature in the nozzle at the lowestplasticizing temperature of the material M, the material in the ejectionorifice will be maintained in a semi-huid, plastic condition and willtherefore not run, ooze or drip from the ejection end of the nozzle whenit is moved out of contact with the mold. After the sprue, runners andcavities of the mold have been emptied, another molding operation may beimmediately performed in the same manner.

Thus, I have provided a novel mechanism and molding method whichovercome and eliminate numerous difficulties encountered in injectionand continuous injection molding of thermoplastic materials. Bypreventing the accumulation of heat in the nozzle and by maintaining thenozzle at an optimum temperature at all times, considerable saving ofthermoplastic material is effected by the elimination of the usualrunning and oozing.

Although I have shown the preferred embodiment of my invention, it is tobe understood that other forms may be adopted, which come within thescope of my invention as set forth in the following claims:

I claim:

1. The method of continuously injecting a thermoplastic material havinga plasticizing temperature only relatively slightly higher than itssetting temperature into a material-receiving mold which comprisespressure feeding said material into a chamber, heating said material insaid chamber to a plasticizing temperature, pressure feeding saidmaterial from said chamber into and through an ejecting nozzle in theform of a substantially restricted passage, removing heat caused byleakage, densication and friction from said nozzle whenever thetemperature of the nozzle rises above the lowest plasticizingtemperature of said material in order to maintain said material in asemi-fluid, plastic condition, and injecting said material at saidtemperature from said nozzle into said material-receiving mold.

2. The method of continuously injecting a thermoplastic material havinga plasticizing temperature only relatively slightly higher than itssetting temperature into a material-receiving mold which comprisespressure feeding said material into a chamber, heating said material insaid chamber to a plasticizing temperature, pressure feeding saidmaterial from said chamber into and through an ejecting nozzle in theform of a substantially restricted passage, removing heat caused byleakage, densification and friction from said nozzle whenever thetemperature of the nozzle rises up to the lowest plasticizingtemperature of said material in order to maintain said material in asemi-uid, plastic condition, and injecting said material at saidtemperature ass- 1,439

JIIOId.

3. The method of continuously injecting va thermoplastic material havinga plasticizing temperature only relatively slightly higher than .itsVsetting temperature into ,a material-.receiving mold which comprisespressure feeding said material into a chamber, heating said material insaid chamber to a plasticizing temperature, pressure feeding saidmaterial from said chamber into and through an electing nozzle in theform of a substantially restricted passage, removing heat causedbyleakage, densification and friction from said nozzle whenever theltemperature of the nozzle rises above a temperature just below thelowest plasticizing temperature of -said mateiral in order to maintain4said material in a semiiluid, plastic condition, and injecting saidmaterial at said temperature from said nozzle into saidmaterial-receiving mold.

4. The method of continuously injecting a thermoplastic material havinga plasticizing temperature only relatively slightly higher than itssetting temperature into a material-receiving mold which comprisespressure feeding said material into a chamber, heating said material insaid chamber to a plasticizing temperature, pressure feeding saidmaterial from said chamber into and through an ejecting nozzle in theform of a substantially restricted passage, removing Yheat caused byleakage, densication and friction from said nozzle whenever thetemperature of the nozzle rises above a temperature between the highestsetting temperature and the lowest plasticizing temperature of saidmaterial in order to maintainsaid material in a semi-fluid, plasticcondition, and injecting said material at said temperature from saidnozzle into said materialreceiving mold.I

5. The method set forth in claim 1 wherein the plasticizing temperatureof the thermoplastic material is up to about 25% higher than the settingtemperature.

6,. The method set forth in claim 1 wherein the plasticizing temperatureof the thermoplastic material is up to about 10% higher than the settingtemperature.

7. The method set forth in claim 1 wherein the thermoplastic materialcomprises a synthetic linear polyamide.

8. In the method of continuously injecting a thermoplastic material intoa material-receiving mold, including the pressure feeding of saidmaterial into and througha .chamber and the heating of said material insaid chamber to a temperature in the range defined by the plasticizingtemperature and the burning temperature of said material, the stepswhich comprise cooling said material to a lower range plasticizingtemperature whenever the temperature of the chamber rises to the rangedefined by the higher range plasticizing temperature and the burningtemperature of the material therein, lpressure feeding said materialfrom said chamber into and through an ejection nozzle in the form of asubstantially restricted passage, removing heat caused by leakage,densication and friction from said nozzle whenever the temperature ofthe nozzle rises above the lowest plasticizing temperature range of saidmaterial, maintaining said material in the outer end of said nozzlepassage in a semi-fluid, plastic condition to prevent running anddripping thereof from said nozzle passage end, and injecting saidmaterial at a temperature between the highest setting temperature andthe lowest plasticizing temperature from said :nozzle into said mold.

`9. The method .of continuously injecting a thermoplasticmaterial havinga plasticizing temperature only relatively slightly higher than itssetting temperature into a material-receiving mold which comprises`pressure feeding said material into a chamber, heating said material insaid :chamber to a plasticizing temperature, pressure feeding saidmaterial from said chamber intoan ejecting nozzle having a slightlyrestricted and elongated passage associated atone end `with said chamberand 'terminating at its ejection end in a transverse abutment wallprovided with va relatively small ejection orifice, accumulatingthermoplastic material in the storage corner rdefined by the passagewall and the abutment `wall to provide an .insulating layer against thetransmission of heat from the nozzle passage to the nozzle ejectionorifice, removing the heat caused by leakage, densication and frictionfrom said orifice Whenever the temperature of said orifice rises abovethe lowest plasticizing temperature of said material, maintaining saidmaterial in a semi-fluid, plastic condition in said orifice, andinjecting said material at said temperature from said nozzle orificeinto said material-receiving mold.

10. 'The method of continuously injecting a thermopastic material havinga plasticizing temperature only relatively slightly higher vthan itssetting temperature into va material-receiving mold which comprisespressure feeding said material into a chamber, heating said material insaid chamber to a plasticizing temperature, pressure feeding saidmaterial from said chamber into :an ejecting nozzle having a .slightlyrestrict- `ed and elongated passage 4associated at one end with saidchamber and terminating at its ejection end in a transverse abutmentWall provided with a relatively small ejection orifice, accumulatingthermoplastic material in the storage corner dened by the passage walland the abutment wall to provide `an insulating layer against thetransmission of heat from the nozzle passage to .the nozzle ejectionorifice, removing heat caused by leakage, densification and frictionfrom said orifice whenever the temperature of said orice rises up to thelowest plasticizing temperature of said material, maintaining saidmaterial in a semi-fluid, plastic condition in said orifice, andinjecting said material at said temperature from said nozzle orificeinto said material-receiving mold.

11. The method of continuously injecting a thermoplastic material havinga plasticizing vtemperature only relatively slightly higher than itssetting temperature into a material-receiving mold which comprisespressure feeding said material into a chamber, heating said material insaid chamber to a plasticizing temperature, pressure feeding saidmaterial from said chamber into an Vejecting nozzle having a slightlyrestricted and elongated passage associated at one end with said chamberand terminating at its ejection end in a transverse abutment wallprovided with a relatively small ejection orifice, accumulatingthermoplastic material in the storage corner defined by the passage walland the abutment wall to provide an insulating layer against thetransmission of heat from the nozzle passage to the nozzle ejectionorifice, removing heat caused by leakage, densification and frictionfrom said orice whenever the temperature of said orifice rises above atemperature just below the lowest plasticizing temperature of saidmaterial, maintaining said material in a semi-fluid, plastic conditionin said orifice, and injecting said material at said temperature fromsaid nozzle orifice into said material-receiving mold.

12. The method of continuously injecting a thermoplastic material havinga plasticizing temperature only relatively slightly higher than itssetting temperature into a material-receiving mold which comprisespressure feeding said material into a chamber, heating said material insaid chamber to a plasticizing temperature, pressure feeding saidmaterial from said chamber into an ejecting nozzle having a slightlyrestricted and elongated passage associated at one end with said chamberand terminating at its ejection end in a transverse abutment wallprovided with a relatively small ejection orice, accumulatingthermoplastic material in the storage corner dened by the passage walland the abutment wall to provide an insulating layer against thetransmission of heat from the nozzle passage to the nozzle ejectionorice, removing the heat caused by leakage, densication and frictionfrom said orifice whenever the temperature of said orice rises above atemperature between the highest setting temperature and the lowestplasticizing temperature of said material, maintaining said material ina semi-fluid, plastic condition in said orice, and injecting saidmaterial at said temperature from said nozzle orifice into saidmaterial-receiving mold.

13. The method set forth in claim 9 wherein the plasticizing temperatureof the thermoplastic material is up to about 25% higher than the settingtemperature.

14. The method set forth in claim 9 wherein the plasticizing temperatureof the thermoplastic material is up to about 10% higher than the settingtemperature.

15. The method set forth in claim 9 wherein the thermoplastic materialcomprises a synthetic linear polyamide.

16. In the method of continuously injecting a thermoplastic materialinto a material-receiving mold, including the pressure feeding of saidmaterial into and through a chamber and the heating of said material insaid chamber to a temperature in the range defined by the plasticizingtemperature and the burning temperature of said material, the stepswhich comprise cooling said material to a lower range plasticizingtemperature whenever the temperature of the chamber rises to the rangedeiined by the higher range plasticizing temperature and the burningtemperature of the material therein, pressure feeding said material fromsaid chamber into an ejection nozzle having a slightly restricted andelongated passage associated at one end with said chamber andterminating at its ejection end in a transverse abutment wall providedwith a relatively small ejection orifice, accumulating thermoplasticmaterial in the storage corner defined by the passage wall and theabutment wall to provide an insulating layer against the transmission ofheat from the nozzle passage to the nozzle ejection orifice, removingheat caused by leakage, densication and friction from said orificewhenever the temperature of said orifice rises above the lowestplasticizing temperature range of said material, maintaining saidmaterial in a semi-huid, plastic condition in said oriiice, andinjecting said material at said temperature from said nozzle orice intosaid material-receiving mold.

17. In an apparatus for the continuous molding of thermoplasticmaterial, including a material-receiving mold, a chamber for receivingand densifying the thermoplastic material and for heating said materialto its plasticizing temperature, a pressure plunger at one end of saidchamber for forcing said material through said chamber and therebydensify said material, an ejecting nozzle structure having a slightlyrestricted and elongated passage associated at one end with the otherend. of said chamber and terminating at its ejection end in a'transverse abutment wail provided with a relatively small ejectionoriiice, said passage wall and said abutment wail defining a storagecorner for the ac cuinulation of an insulating layer of 'thermoplasticmaterial to prevent the transmission of heat from said nozzle passage tosaid nozzle ejection orifice, heat-transferring means including acooling passage disposed adjacent said ejection orifice and adapted toprovide for the iow of a coolant fluid therethrough, regulating meansresponsive to the temperature of the nozzle orifice for controlling therate of iiow of the coolant iiuid into said coolant passage whenever thetemperature of the nozzle oriice rises above the lowest plasticizingtemperature of the thermoplastic material to remove excess accumulatingheat caused by leakage, densification and friction oi the material inthe nozzle passage, thereby maintaining the material in the orice in asemi-fluid, plastic condition.

18. The combination set forth in claim 17, wherein the cooling passageis positioned adjacent and above the ejection orice.

19. The combination set forth in claim 17, wherein the cooling passageis positioned above the ejection orifice and adjacent both the ejectionorice and the abutment wall.

GEORGE J. KOVACS.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,043,584 Husted June 9, 19362,111,857 Jeery Mar. 22, 1938 2,309,729 Gordon Feb. 2, 1943 2,344,176Shaw Mar. 14, 1944

